In LTE (Long Term Evolution) systems specified in the 3GPP (3rd Generation Partnership Project), a reference signal (RS) is arranged in a resource block (RB). For example, a mobile terminal device receives the reference signal, and is thereby capable of performing coherent detection (Non-patent Document 1). The reference signal is scrambled (randomized by a known signal sequence) by a cell-specific scrambling signal.
The 3GPP has studied LTE-A (LTE-Advanced) systems to actualize high-speed transmission in wider coverage than in the LTE system. In the LTE-A system, two types of reference signals (Demodulation Reference Signal (DM-RS) and channel quality measurement reference signal (CSI-RS)) are specified in downlink.
The demodulation reference signal is used in demodulation of the Physical Downlink Shared Channel (PDSCH). The demodulation reference signal is subjected to the same precoding as in the PDSCH and is transmitted to a mobile terminal device. The channel quality measurement reference signal is used in measuring channel quality information (Channel State Indicator) that the mobile terminal device transmits to the radio base station apparatus as feedback.